I must admit, lowering the cap for members with more that 20 posts seems like it could be a reasonable answer, However I completely disagree with limiting where new members can post, That will only drive them away.
My standing on this subject is that the cap does not need to be lowered, As I did not even know it existed until I read this thread. When I post in a thread I read multiple pages worth of posts, to get a feeling for the conversation. that alone usually takes 2 minutes, and if it is not my first post in a thread, I still take a few minutes to think of my response, and type it out. So in my opinion anyone who regularly trips the cap is most likely a spammer or not thinking their post through.